Instruction manual
–
AQ G3x7 Generator protection IED
112 (211
)
Calculation method Calc(D):
If the voltage is below the minimal level, then the VOLT_OK_LOW status is “false” but if
there are voltage samples stored in the memory for 80 ms, then the direction is decided
based on the sign either of the real part of the impedance or that of the imaginary part of
the impedance, whichever is higher.
R, X=f(u, i) direction = f(max{R(Umem, i), X(Umem,i)})
Calculation method Calc(E):
If no directional decision is required, the decision is based on the absolute value of the
impedance (forward fault is supposed)
R=abs(R), X=abs(X)
Calculation method Calc(F):
If the voltage is not sufficient for a directional decision and no stored voltage samples are
available, the impedance is set to a high value:
R=1000500, X=1000500
3.2.21.3
Offset circle characteristics
The operate decision is based on offset circle characteristics.
The calculated R
1
and X
1
=
ϖ
L
1
co-ordinate values define six points on the complex
impedance plane for the six possible measuring loops. These impedances are the positive
sequence impedances. The protection compares these points with the
„ offset circle”
characteristics of the impedance protection, shown in figures below. The main setting
values of “Rcompaund” and “Xcompaund” refer to the positive sequence impedance o
f the
fault loop, including the fault positive sequence resistance of the possible electric arc and,
in case of a ground fault, the tower grounding positive sequence resistance as well. (When
testing the device using a network simulator, the resistance of the fault location is to be
applied to match the positive sequence setting values of the characteristic lines.)